Patent GB-313664-A (GB)
Title: Improvements in or relating to electric motors
IPC: H02K27/10
Filed: 1928-03-20
Abstract: 313,664. White, A. E., (Leland Electric Co.). March 20, 1928. Alternating-current commutator machines; brush holders; casings and frames. - A motor, especially of the repulsion-induction type, has a speed-controlled brush-lifting mechanism comprising a brush-supporting member to which the brush is rigidly secured and which is adapted to be engaged by an actuating member on the attainment of a predetermined motor speed to lift the brushes, the brush-supporting member being movable relatively to the actuating member when this member is inoperative. In addition, a centrifugally acting commutator shortcircuiting device may be provided, together with yielding means between the machine body and its supporting standards to prevent the transmission of torsional vibrations to the supporting structure. The standards 7, Figs. 1 and 3, have their upper ends formed as two separate curved arms 9 between which the bearing housings 10 of the main motor frame are inserted, the housings and standards having annular surfaces or races between which endless springs 12 are introduced. These springs carry the weight of the motor and take up torsional vibrations and to some extent radial movements of the motor; and their frictional engagement with the races prevents relative movement between the motor frame and standards under normal torque. Slipping during abnormal torque is prevented by springs 13 which are interposed between the standards and abutments 14 on the motor casing. The commutator short-circuiting and brushlifting gear are shown in Figs. 6 and 8, Fig. 8 being a section on the line 8-8 in Fig. 6. Fig. 10 shows the brushes in their raised position. The short-circuiting is effected by centrifugally operated weights 19 moving between a plate 20 and the commutator support 6, against the action of a contractile band 23, and limited in their outward travel by a flanged plate 63. The weights are preferably loosely secured together in groups by links 27 at their inner ends so that at a limiting speed the groups move out radially and spread slightly fanwise, the contacts between the commutator segments and projections 21 on the weights giving the short-circuit. The groups are connected by intervening plates 25 provided with lugs 28 which project through slots in the retaining disc 20 and enter the slots 51, Fig. 6, in the brush-lifting weights 48 described below, thus causing synchronous action of the two sets of centrifugal weights. The brush arms 31 are pivoted at 32 under the pressure of a band spring 34 and are raised from the normal position. Fig. 6, to that shown in Fig. 10, by lifting devices, comprising plates 36 with lugs 40 protruding into curved slots 41 in the brush arms which are concentric with the stud 32 and allow movement of the brush arms about the pivot 32 without regard to the brush-lifting mechanism. The lifters 36, which have. a pivotal abutment at 37 and are pressed together by a spring 38, enclose an actuating stud 43 and this, by means of toggle links 44, is coupled to the lifters. Thus, radial outward movement of the stud first separates the outer ends of the lifters, thereby rocking them and causing the lugs 40 to grip the brush arms, and then lifts the arms awav from the commutator. The stud is mounted on a lever 45 (shown in dotted lines in Fig. 6) which is pivoted at 46 on the supporting bracket 39 and has a channelled extension 47 whereby the movement of centrifugally-acting weights 48 is transmitted to the stud 43 and the brush arms. These weights move between the plate 20 and an outer plate 50 and have bent outer ends 49 running within the channel 47, the arrangement being such that when the stud has lifted the brushes from the commutator the action of the spring 38 on the lifters 36 moves the stud slightly further and so carries the channel 47 clear of contact with the flanges 49 of the weights 48. To ensure that the weights all move together, they are formed with bent ends 55, Fig. 6, entering a notched ring 52, rotatably mounted on the armature shaft, and with interlocking projections 57 and recesses 50. The projection of the lugs 48 of the short-circuiting weights through the slots 51 in the weights 48 ensures simultaneous movement of both sets of weights and also allows the single contractile band 23 to be used for both sets.